Heat a large pot over medium-high heat and add the sausage, breaking it into small pieces as it cooks. Once the sausage is mostly browned, add the diced onion and cook for another 3-4 minutes, stirring occasionally, until the onion softens slightly and begins to caramelize at the edges. This browning creates a flavorful foundation for the entire soup and develops deep, savory notes that will carry through the final dish.

Reduce heat to medium-low and add the minced garlic, cooking for about 30 seconds until fragrant. Add the dried basil, oregano, parsley, thyme, and red pepper flakes, stirring constantly for 1 minute. This blooming step releases the essential oils in the dried herbs, intensifying their flavors throughout the soup. I find that blooming spices in fat makes a noticeable difference—it's worth the extra minute.

In a small bowl, whisk together the tomato paste with 1/2 cup of the beef broth until smooth, breaking up any lumps. This prevents the tomato paste from clumping when added to the hot pot. Pour this mixture into the pot along with the remaining beef broth, vegetable broth, and fire-roasted tomatoes (with their juices). Stir well to combine, then increase heat to high and bring the soup to a boil.

Once the soup reaches a boil, reduce heat to medium and let it simmer for 5 minutes to allow the flavors to meld. Add the refrigerated tortellini and simmer for 10-15 minutes, or until the tortellini float to the surface and are tender but still have a slight firmness to the bite. I always use refrigerated tortellini rather than frozen because it has a better texture and cooks more evenly in the broth.

Remove the pot from heat and stir in the arugula, which will wilt into the warm soup in about 30 seconds, adding a fresh, slightly peppery note that balances the richness of the sausage and cheese. Taste the soup and season with salt and pepper as needed. Ladle into bowls and finish each serving with a generous shower of freshly grated Parmesan cheese.